Compact disks (CDs) are well known; there is a variety of types of compact disks. For instance, CDROMs typically hold computer programs and data. There are also audio compact disks which hold music, etc. and video compact disks for material such as movies. Each type of compact disk has an associated player. There are a variety of compact disk standards.
Compact disks are a digital storage media, unlike conventional videotape. Therefore copies of such digital material contain all of the information of the original and are a frequent target for pirates (copyright infringers) who make unauthorized copies or otherwise misuse same. There have been developed a number of security systems to prevent unauthorized copying in the compact disk field.
The present invention is directed to a particular aspect of the security problem of compact disks including video CDs and CDROMs (data CDs). Specifically, there is a need for a compact disk player that only plays proprietary CDs, does not play standard CDs, where the proprietary CDs cannot be copied and the proprietary CDs do not play on standard CD players. Thus this is a “closed” system involving proprietary (in terms of the format) CDs and associated players. A typical application is for a toy system where there is no need to play generally available CDs but only the toy system's CDs are of interest.
Any such system must be relatively inexpensive to implement (since these are consumer players), and must be robust so as to prevent copying, and not interfere with playing and enjoyment of the CD program material. The cost requirement is especially restrictive since even a few dollars of added cost are problematic in consumer electronics. Therefore, well-known methods such as encryption may be problematic since they may require inclusion in the player of a dedicated decryption integrated circuit. Since the decryption must be performed in real time, software decryption is generally less useful in this context.